The 23-year-old Briton was detained Thursday at a cybersecurity conference in Las Vegas after a sting operation on accusations he created and sold the Kronos virus, which steals banking details.
"He admitted he was the author of the code of Kronos malware and indicated he sold it," prosecutor Dan Cowhig told a US federal court in Nevada, according to The Guardian newspaper.
Cowhig objected to an order by the federal judge to release Hutchins on $30,000 bail, saying he presented a danger to the public. His defense lawyers reportedly said he planned to plead not guilty.
The security expert was called a hero by British media after he found a "kill-switch" in the WannaCry ransomware code that hit millions of computers around the globe in May and caused massive disruption in British healthcare.
